Differentiating circuits



Feb. 22, 1955 BESS 2,702,855

DIFFERENTIATING CIRCUITS Filed Feb. 1, 1946 OUTPUT L I OUTPUT INPUT INVENTOR. LEON BESS ATTORNEY United States Patent DIFFERENTIATIN G CIRCUITS Leon Bess, Urbana, Ill., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application February 1, 1946, Serial No. 644,976

1 Claim. (Cl. 250-27) This invention relates to wave shaping circuits, and more particularly to differentiating circuits utilizing the feedback of an electron tube to provide shorter effective time constants.

Heretofore the minimum time constant of differentiating or peaking circuits has been limited by stray capacitance and the size of resistances necessary for normal functioning of electronic circuits, with the attendant difficulty that sufficiently sharp peaking action could not be obtained.

The general object of the present invention is to overcome the foregoing difficulties.

Another object of the present invention is to provide a differentiating circuit producing sharp peaking action.

A further object is to provide a differentiating circuit utilizing the feedback of an electron tube to reduce the effective capacitance of the differentiating circuit.

A still further object is to provide a differentiating circuit utilizing the feedback of an electron tube to reduce the effective resistance of the differentiating circuit.

These and other objects will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a schematic diagram of one form of the invention; and

Fig. 2 is a schematic diagram of another form of the invention.

Referring to the drawing, and more particularly Fig. 1, a differentiating circuit is disclosed having input terminals 38 and 39 for a voltage wave to be differentiated, and providing a differentiated voltage wave at the output terminals 51 and 52. Input terminal 38 is connected to grid 33 of an electronic amplifier 31. The output at plate 32 of this amplifier is applied to an RC coupling or peaking circuit comprising a condenser 16 and resistors 17, 18, and 19. The output of this RC circuit is connected to output terminal 51 and also to grid 13 of an electron tube 11. The cathode 14 of tube 11 is connected back to the input of the RC coupling circuit to provide feed back which reduces the effective capacity of the circuit.

Plate 32 of electron tube 31 is connected to a source of positive potential at terminal 36 through resistor 17 which constitutes the input to the above mentioned RC coupling circuit. Plate 12 of tube 11, the feedback tube, is connected directly to a source of positive potential at terminal 36. Resistors 18 and 19, in addition to being the output of the RC circuit, constitute a voltage divider determining the operating point of tubes 11 and 31.

2,702,855 Patented Feb. 22, 1955 It is obvious from Fig. 1 that tube 11 provides feedback to assist any action at the output terminal 51. It can be shown that the effective capacitance of the RC cir cuit is reduced by a factor approximately proportional to the transconductance of tube 11. This reduction of capacitance is independent of stray capacity, a condition not obtained in a conventional differentiating circuit where the minimum capacitance is limited by stray capacity.

Referring to Fig. 2 another differentiating circuit is disclosed which is similar to that of Fig. 1 and has input terminals 48 and 49 and output terminals 55 and 56. Input terminal 48 is connected to grid 43 of a cathode follower 41. The output at cathode 44 of this tube is connected to the input of an RC coupling or differentiating circuit comprising condenser 26, resistors 27 and 28, and indirectly resistor 29. The output of this RC circuit is applied to cathode 24 of electron tube 21, a grounded grid amplifier. Applying the input to the cathode of tube 21 produces feedback which has the effect of reducing its input resistance thereby reducing the resistance of the RC circuit. The resistance of this RC circuit is further reduced by the use of a cathode follower at its input.

Plate 42 of electron tube 41, the cathode follower, is directly connected to a source of positive potential at terminal 46. Plate 22 of electron tube 21 is connected to output terminal 55 and to a source of positive potential at terminal 46 through resistor 29.

It can be shown that the input resistance of electron tube 21 is reduced by a factor approximately proportional to the effective transconductance of tube 21. Thus the effective resistance of the aforementioned RC circuit has been reduced while still using resistors of sufficient size for normal functioning of electron circuits. Also the use of a grounded grid amplifier 21 reduces the effect of its grid to plate capacitance.

The invention described in the foregoing specification need not be limited to the details shown, which are consitliiered to be illustrative of two forms the invention may ta e.

What is claimed is:

A wave shaping circuit comprising, first and second electron tubes each having an anode, a cathode and a control grid, a source of potential, a first resistor connecting the anode of said first tube to the positive terminal of said source of potential, second and third resistors serially connected in parallel with said first tube and said first resistor, a condenser connected between the anode of said first tube and the junction of said second and third resistors, said second tube being connected in parallel with said first resistor with its control grid connected to the junction of said second and third resistors, and a pair of output terminals connected across said third resistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,235,131 Wheeler Mar. 18, 1941 2,251,973 Beale et a1 Aug. 12, 1941 2,324,797 Norton July 20, 1943 2,403,616 Sanders, Jr. July 9, 1946 2,496,337 De Boisblanc Feb. 7, 1950 

